Last week, the U.S. Supreme Court (SCOTUS) held that law enforcement officials cannot attach GPS tracking devices to individuals’ vehicles without a warrant.

In United States v. Jones, the Court was faced with whether Antoine Jones’ conviction for drug trafficking should be upheld where law enforcement officials obtained a warrant to attach a GPS device to Jones’ wife vehicle but didn’t attach the device within the required 10 days. With information later obtained from the tracking device, officers arrested Jones, which resulted in the underlying conviction in the case.

The U.S. Court of Appeals for the District of Columbia Circuit overturned Jones’ conviction, and all nine justices on SCOTUS agreed — though they differed on the rationale behind the decision.

The majority, which included Chief Justice John Roberts, and Justices Antonin Scalia, Anthony Kennedy, Clarence Thomas, and Sonia Sotomayor viewed the tracking without a valid warrant as a violation of the Fourth Amendment, which protects individuals from unreasonable searches and seizures.

Meanwhile, concurring Justices Samuel A. Alito, Ruth Bader Ginsburg, Stephen Breyer, and Elena Kagan focused on Jones’ “reasonable expectation of privacy” and whether it had been violated, with Alito noting that “the use of longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.”

Scalia, writing for the majority, countered that the “reasonable expectation of privacy” standard simply didn’t need to be employed in this case because the decision could be reached through a finding that GPS tracking is considered a “search” under the law, which requires a warrant.

Although privacy advocates have applauded the overall ruling, some are dismayed by what SCOTUS didn’t say.

“The case was an opportunity for the court to announce that round-the-clock surveillance of citizens without a warrant offends Fourth Amendment guarantees,” writes Renée Hutchins at The Baltimore Sun.

Lori Andrews, a professor at the Chicago-Kent College of Law, [said] the decision ‘provides little guidance about which activities might be considered searches, which require warrants, and which voluntary disclosures to third parties might waive Fourth Amendment rights.’